Iterating vertex of every frame in Blender
The mesh data always contains the original locations of vertices. Not sure if it is the only way but you can use object.to_mesh to get a copy of the mesh data that is deformed.

import bpy

obj = bpy.context.active_object
scn = bpy.context.scene

mod_mesh = obj.to_mesh(scn, True, 'RENDER')

for v in mod_mesh.vertices:
    print(v.co)


Note that this creates a new mesh object, so as you are iterating over each frame you will want to remove each copy as you go with -

bpy.data.meshes.remove(mod_mesh)